Charged particle beam apparatus permitting high resolution and high-contrast observation

ABSTRACT

A lower pole piece of an electromagnetic superposition type objective lens is divided into an upper magnetic path and a lower magnetic path. A voltage nearly equal to a retarding voltage is applied to the lower magnetic path. An objective lens capable of acquiring an image with a higher resolution and a higher contrast than a conventional image is provided. An electromagnetic superposition type objective lens includes a magnetic path that encloses a coil, a cylindrical or conical booster magnetic path that surrounds an electron beam, a control magnetic path that is interposed between the coil and sample, an accelerating electric field control unit that accelerates the electron beam using a booster power supply, a decelerating electric field control unit that decelerates the electron beam using a stage power supply, and a suppression unit that suppresses electric discharge of the sample using a control magnetic path power supply.

CLAIM OF PRIORITY

This application is a Continuation of U.S. application Ser. No.13/551,452 filed on Jul. 17, 2012, which is a Continuation of U.S.application Ser. No. 12/385,612 filed on Apr. 14, 2009. Priority isclaimed based on U.S. application Ser. No. 13/551,452 filed on Jul. 17,2012, which claims the priority of U.S. application Ser. No. 12/385,612filed on Apr. 14, 2009, which claims priority from Japanese patentapplication JP 2008-104232 filed on Apr. 14, 2008, the content of whichis hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a charged particle beam applicationapparatus, or more particularly, to a charged particle beam applicationapparatus that is used to observe, inspect, and analyze a wafer sample,which has a minute circuit pattern, with a high resolution using alow-acceleration electron beam.

2. Description of the Related Art

Various techniques have been employed in detecting a defect which occursin fabrication of a microscopic circuit such as an LSI, measuring thelength of the defect, or assessing the shape of the defect. For example,an optical inspection apparatus produces an optical image of themicroscopic circuit and inspects the image to detect an abnormality.However, the resolution of the optical image is not high enough toidentify a very small shape-related feature, and is not high enough todiscriminate a harmful defect from a harmless defect in terms offabrication of a circuit. A sample to be handled by such ameasurement/inspection apparatus has become more and more microscopicalong with advancement of technologies. For example, in a recent DRAMmanufacturing process, the width of a metal wire is 90 nm or less. For alogic IC, a gate dimension has reached 45 nm.

A defect inspection technique using an electron beam provides aresolution that is high enough to image a microscopic shape-relatedfeature of a contact hole, a gate, or a wire and a shape-related featureof a microscopic defect, and can therefore be used to classify or detecta grave defect on the basis of a contrast of a shaded image of adetective shape. Therefore, for measurement/inspection of a microscopiccircuit, a measurement/inspection technique employing a charged particlebeam has an advantage over the optical inspection technique.

A scanning electron microscope (SEM) that is a type of charged particlebeam apparatus focuses a charged particle beam emitted from an electronsource of a heating type or a field emission type so as to form a thinbeam (probe-like beam), and sweeps the probe-like beam over a sample.Secondary charged particles (secondary electrons or reflected electrons)are emitted from the sample due to the sweep. Synchronously with thesweep of the primary charged particle beam, a scan image is acquired byusing the secondary charged particles as a luminance signal of imagedata. A typical scanning electron microscope accelerates electronsemitted from the electron source using an extracting electrodeinterposed between the electron source, at which a negative potential isdeveloped, and a ground at which a ground potential is developed, andirradiates the resultant electrons to the sample.

The resolution offered by a scanning charged particle microscope such asan SEM and the energy of a charged particle beam have a closerelationship. When a primary charged particle beam of high energyreaches a sample (that is, when the landing energy of a primary chargedparticle beam is large), since primary charged particles deeply invadeinto the sample, an emissive range on the sample from which secondaryelectrons and reflected electrons are emitted expands. As a result, theemissive range becomes wider than the probe diameter of the chargedparticle beam, and an observational resolution is markedly degraded.

When the energy of a primary charged particle beam is excessivelyreduced in order to lower the landing energy, the probe diameter of thecharged particle beam greatly increases due to aberrations. Eventually,the observational resolution is degraded.

Further, a contrast of an SEM image is affected by the value of acurrent carried by a primary charged particle beam to be irradiated to asample. When the beam current decreases, the ratio of a secondary signalto a noise (signal-to-noise ratio) is greatly lowered and a contrast ofa scan image is degraded. Preferably, the beam current value should becontrolled to be as large as possible. When the energy of the primarycharged particle beam is reduced, formation of a thinner probe-like beambecomes hard to do due to the Coulomb's law. When the energy of theprimary charged particle beam is excessively controlled to become small,a beam current required for producing the scan image becomesinsufficient. This makes it hard to acquire the scan image with a highmagnification and a high resolution.

For observation with a high resolution, the energy of a primary chargedparticle beam, or especially, landing energy has to be appropriatelycontrolled according to an object of observation.

As a control technology for landing energy, a retarding method is widelyadopted. In the retarding method, a potential causing a primary chargedparticle beam to decelerate is developed at a sample in order todecrease the energy of the charged particle beam to a desired level ofenergy immediately before the charged particle beam reaches the sample.

For example, in JP-A-6-139985, an invention that controls the timing, atwhich a negative potential for retarding is developed at a sample,responsively to mounting or replacement of a sample has been disclosed.

An invention disclosed in JP-A-2001-185066 is such that: when the slopeof a sample is observed according to the retarding method, the magneticpoles of an objective lens are separated into upper and lower ones, anda potential identical to the one at the sample is developed at the lowermagnetic pole in efforts to minimize the adverse effect of an asymmetricretarding electric field derived from the slope of the sample (tominimize occurrence of astigmatism or reduction in efficiency indetecting secondary electrons).

In JP-A-6-260127, an invention of a potential measurement apparatusemploying an electron beam has been disclosed. In the potentialmeasurement apparatus described in JP-A-6-260127, an objective lens isdivided into a yoke part for excitation and a magnetic-pole part, and isformed with two magnetic circuits. An electric field for pulling upsecondary electrons is applied to the magnetic-pole part. According toJP-A-6-260127, since the objective lens is divided into two parts, themagnetic circuits can be readily designed according to the workingdistance between a sample and the objective lens. The diameter of thespot of an electron beam can be appropriately controlled irrespective ofthe working distance.

SUMMARY OF THE INVENTION

A contrast of a charged particle beam image is affected by an amount ofcurrent carried by a charged particle beam. In order to acquire ahigh-contrast scan image, the amount of beam current has to beincreased. However, if the amount of beam current increases, a probediameter expands due to the Coulomb's law. In order to focus a spreadbeam on a sample, an objective lens whose lens action is intense isneeded. In the case of a magnetic-field type objective lens that narrowsa beam by causing a magnetic field to leak out to the ray axis of aprimary charged particle beam, a magnitude of excitation has to beincreased in order to intensify the lens action.

However, as long as a magnetic field type objective lens has theconventional structure, even if a magnitude of excitation is increased,an expected lens action cannot be exerted. A magnitude of a magneticflux occurring in a magnetic path in the objective lens is restricted bymagnetic saturation. The saturated magnetic flux density in the magneticpath is determined with a magnetic material made into the magnetic path.Therefore, even if the magnitude of the magnetic flux occurring in themagnetic path increases, a magnetic flux unacceptable by the magneticpath leaks out from any part of the magnetic path. As a result, the lensaction is not so intensified as the increase in the magnitude ofexcitation. In particular, when an accelerating voltage for a chargedparticle beam is increased, if a probe-like beam of high energy isproduced, an incident that the beam cannot be focused may take place.Further, when a magnetic flux leaks out to the trajectory of secondarycharged particles, the number of secondary charged particles reaching adetector decreases. Eventually, the quality of an acquired scan imagedeteriorates. When a magnitude of a magnetic flux is distributed alongthe axis of a beam, a lens action is exerted. Therefore, in order toapproach a site of action of the lens to a sample, when a magnitude of amagnetic flux is increased, a magnetic flux distribution is developednear the desired site of action at the same time. Thus, the magneticflux distribution has to be prevented from spreading to an axialposition away from the site of action.

A resolution offered by a charged particle beam apparatus is determinedwith the probe diameter of a beam. When the energy of a charged particlebeam decreases, the probe diameter increases due to chromatic aberrationand the resolution is degraded. What is referred to as the chromaticaberration is an aberration attributable to a velocity distribution of acharged particle beam emitted from an electron source. In the retardingmethod, if a position at which the charged particle beam is deceleratedis approached to the sample, the adverse effect of aberrations can belessened. Therefore, when an apparatus is designed, the working distanceof an objective lens is designed to be as short as possible.

However, since an objective lens and a sample into must not bephysically brought into contact with each other, a technique forlessening the adverse effect of aberrations by decreasing the workingdistance of the objective lens has its limitations. In the case of theretarding method, since there is a large potential difference betweenthe sample (or a sample stage) and objective lens, if the workingdistance is made too short, there is a risk that the sample may bedestroyed with electric discharge.

The inventions described in JP-A-6-139985, JP-A-2001-185066, andJP-A-6-260127 are intended to provide an electron microscope thatacquires a high-contrast and high-resolution observation image. Formeasurement or inspection of a microscopic circuit for which the ongoingapparatuses are designed, even when an apparatus is produced using theconventional technology described in any of JP-A-6-139985,JP-A-2001-185066, and JP-A-6-260127, basic performance such as acontrast or a resolution is insufficient. In particular, when it comesto semiconductor devices fabricated using a micro-machining technology,a signal generated from a concave part such as a contact hole or a linepattern is so feeble that observation of a microscopic object ormeasurement of a length is terribly hindered.

The present invention provides a charged particle beam apparatus thatadopts a retarding method and a magnetic field type objective lens for acharged particle optical system. In the charged particle beam apparatus,a lower magnetic pole member of an objective lens is divided into upperand lower stages. The potential at a magnetic pole member on a sampleside of the divided lower magnetic pole member is controlled into anintermediate potential between the potential at a magnetic pole memberon a side far away from a sample and the potential at the sample. Thus,the charged particle beam apparatus can detect a high-contrast andhigh-resolution secondary-charged particle signal. Preferably, thepotential at the magnetic pole member on the sample side is controlledto be equal to the potential at the sample.

Since the lower magnetic pole member is divided into the upper and lowerstages, an induced magnetic flux is concentrated on the distal part ofan upper magnetic pole member (upper pole piece) and the distal part ofthe lower magnetic pole member (lower pole piece). This is attributableto the fact that when the lower pole piece is placed adjacently to thesample, the magnetic flux extending from the upper pole piece to thelower pole piece can be concentrated on the sample. The division of themagnetic pole member makes it possible to form an objective lens thatexerts a greater lens action than a conventional objective lens does.The magnetic pole member on the sample side alleviates a potentialgradient between the bottom of the objective lens and the sample, andacts as means for suppressing electric discharge of the sample.

Owing to the present invention, an objective lens that exerts asatisfactory lens action on a primary charged particle beam having alarge amount of beam current and requiring a high accelerating voltagecan be manufactured. Eventually, a charged particle beam apparatusoffering a high contrast and a high resolution can be realized. Sincethe charged particle beam apparatus offering a high contrast and a highresolution can be realized, a charged particle beam applicationapparatus permitting observation of a microscopic defect, measurement ofa length, and assessment of a shape can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an overall constitution diagram of a charged particle beamapparatus of an embodiment 1;

FIG. 1B is a perspective view of an objective lens included in theembodiment 1;

FIG. 2 shows magnetic-field distributions on the optical axes of theobjective lens in the embodiment 1 and a conventional objective lens;

FIG. 3 shows the relationship between the shortest focal length andlanding energy;

FIG. 4 is an overall constitution diagram of a charged particle beamapparatus of an embodiment 2;

FIG. 5 is an overall constitution diagram of a charged particle beamapparatus of an embodiment 3;

FIG. 6A is an overall constitution diagram of a charged particle beamapparatus of a variant of the embodiment 3;

FIG. 6B is a perspective view of an objective lens included in thevariant of the embodiment 3;

FIG. 7A is an overall constitution diagram of a charged particle beamapparatus of an embodiment 4; and

FIG. 7B is a perspective view of an objective lens included in theembodiment 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For brevity's sake, in relation to embodiments to be described below,examples in which the present invention is applied to an apparatus usinga scanning electron microscope will be mainly described. Anelectromagnetic superposition type objective lens in each of theembodiments can be generally adapted to charged particle beamapparatuses including an electron beam apparatus and an ion beamapparatus. In the embodiments to be described below, apparatuses thatdeal with a semiconductor wafer as a sample will be described. As forsamples to be dealt with by various types of charged particle beamapparatuses, in addition to the semiconductor wafer, various samplesincluding a semiconductor substrate, a fragment of a wafer having apattern formed therein, a chip cut out from the wafer, a hard disk, anda liquid crystal panel can be regarded as objects of inspection ormeasurement.

Embodiment 1

In relation to an embodiment 1, an example in which the presentinvention is applied to a scanning electron microscope will be describedbelow.

FIG. 1A is an illustrative diagram showing an overall constitution of ascanning electron microscope. The scanning electron microscope of thepresent embodiment includes: an electron optical system 102 formed in avacuum housing 101; an electron optical system control device 103disposed on the perimeter of the electron optical system; a hostcomputer 104 that controls control units included in respective controlpower supplies, and controls the whole of the apparatus on a centralizedbasis; an operator console 105 connected to the control device; anddisplay means 106 including a monitor on which an acquired image isdisplayed. The electron optical system control device 103 includes apower supply unit that feeds a current or a voltage to each of thecomponents of the electron optical system 102, and signal control linesover which control signals are transmitted to the components.

The electron optical system 102 includes: an electron source 111 thatproduces an electron beam (primary charged particle beam) 110; adeflector 112 that deflects the primary electron beam; anelectromagnetic superposition type objective lens 123 that focuses theelectron beam; a booster magnetic path member 116 that focuses ordiffuses secondary particles 115 emitted from a sample 114 held on astage; a reflecting member 118 with which the secondary particlescollide; and a central detector 122 that detects collateral (tertiary)particles reemitted due to the collision. The reflecting member 118 isformed with a disk-shaped metallic member having a passage opening for aprimary beam formed therein. The bottom of the reflecting member 118realizes a secondary-particle reflecting surface 126.

An electron beam 110 emitted from the electron source 111 is accelerateddue to a potential difference developed between a extracting electrode130 and an accelerating electrode 131, and routed to the electromagneticsuperposition type objective lens 123. The objective lens 123 focuses anincident primary electron beam on the sample 114.

Referring to FIG. 1B, the internal structure of the electromagneticsuperposition type objective lens 123 included in the present embodimentwill be detailed below. In FIG. 1B, in addition to the internalstructure of the electromagnetic superposition type objective lens 123,the sample 114 to be measured or inspected is shown.

The electromagnetic superposition type objective lens 123 in the presentembodiment includes at least: three members, that is, a yoke member 132disposed around the ray axis of a primary electron beam (or the centeraxis of the electron optical system 102), the booster magnetic pathmember 116 disposed in a space between the yoke member 132 and the rayaxis of the primary electron beam, and a control magnetic path member133 disposed in a closed space defined between the bottom of the yokemember 132 and the sample 114; and a coil 134. The ray axis of theprimary electron beam or the center axis of the electron optical system102 is often aligned with the center axis of the electromagneticsuperposition type objective lens 123 or vacuum housing 101.

The yoke member 132 in FIG. 1B is formed with a hollowed annular member,and the section of the yoke member 132 is shaped like a trapezoid havingthe side thereof, which is opposed to the ray axis of the primaryelectron beam, inclined. In the electromagnetic superposition typeobjective lens in the present embodiment, the yoke member is disposed sothat the ray axis of the primary electron beam will pass through thecenter of the annular member. The coil 134 is sustained inside the yokemember 132 that is the annular member. A magnetic flux to be used tofocus the primary electron beam is excited by the coil. A space isformed on the internal surface side of the bottom of the trapezoidalshape (the side opposed to the primary electron beam). Owing to thespace, the excited magnetic flux does not form a closed magnetic path inthe yoke member 132 but extends to the booster magnetic path member 116and control magnetic path member 133. An opening through which theprimary electron beam passes is formed in the top of the yoke member 132(a falling direction of the primary electron beam) and in the bottomthereof (an emitting direction of the primary electron beam). A softmagnetic material is adopted as the material of the yoke member.Although the yoke member 132 shown in FIG. 1B is realized with theannular member having a trapezoidal section, as long as the capabilityto transfer the excited magnetic flux to the booster magnetic pathmember 116 and control magnetic path member 133 is exerted, the shape ofthe yoke member 132 is not limited to any specific one. For example, thesection of the yoke member may be shaped like a bracket.

The booster magnetic path member 116 is a cylindrical (or conical)member formed along the internal surface (area opposed to a primaryelectron beam) of the annular member realizing the yoke member 132. Thebooster magnetic path member 116 is disposed in the electromagneticsuperposition type objective lens so that the center axis of thecylinder will be aligned with the ray axis of the primary electron beam(or the center axis of the vacuum housing 101). As the material, a softmagnetic material is adopted as it is for the yoke member 132. The lowerdistal end of the cylinder (the distal part of the side thereof opposedto the sample) acts as a magnetic pole (pole piece) on which a magneticflux excited by the coil is concentrated.

The control magnetic path member 133 is disposed on the side of thebottom of the yoke member 132. The control magnetic path member 133 is adisk-like or conical soft magnetic plate having an opening, throughwhich the booster magnetic path is extended, in the center thereof. Theyoke member 132 is disposed to have the axis thereof aligned with theray axis of a primary electron beam in the electromagnetic superpositiontype objective lens. The opening edge of the control magnetic pathmember 133 realizes a magnetic pole on which a magnetic flux isconcentrated. If a magnetic flux is concentrated on a gap between themagnetic pole of the control magnetic path member 133 and the magneticpole of the booster magnetic path member 116, a lens effect that isgreater than a conventional one can be exerted on a primary electronbeam. A pole piece belonging to the booster magnetic path member may becalled an upper magnetic pole, and a pole piece belonging to the boostermagnetic path member may be called a lower magnetic pole.

Not only the control magnetic path member 133 and booster magnetic pathmember 116 but also the yoke member 132 and control magnetic path member133 and the yoke member 132 and booster magnetic path member 116 arespatially separated from each other with a predetermined gap betweenthem. However, the yoke member 132, control magnetic path member 133,and booster magnetic path member 116 are magnetically intensivelycoupled to one another. A magnetic flux excited by the coil 134penetrates through the magnetic path members. The distal part of theobjective lens in which the booster magnetic path member 116 and controlmagnetic path member 133 adjoin is formed to be so thin as to have athickness of 3 mm or less in order to concentrate the magnetic fluxadjacently to the sample. The proximal part of the objective lens inwhich the booster magnetic path member 116 adjoins the yoke member 132is formed to have a thickness of 1 cm or more in order to avoid magneticsaturation.

Next, potentials to be developed at the booster magnetic path member116, yoke member 132, and control magnetic path member 133 will bedescribed below. The yoke member 132, control magnetic path member 133,and booster magnetic path member 116 are electrically isolated from oneanother with an insulating material between each pair of them. A voltagethat causes the potential at the booster magnetic path member 116relative to the potential at the yoke member 132 to be positive and thatcauses a potential difference from the potential at the acceleratingelectrode 131 to be positive is applied to the booster magnetic pathmember 116. The voltage is fed from a booster power supply 135. The yokemember 132 is retained at a ground potential. Therefore, the electronbeam 110 passes through the booster magnetic path member 116 while beingmost greatly accelerated on the trajectory thereof due to the potentialdifference between the accelerating electrode 131 and booster magneticpath member 116.

Even in the charged particle beam apparatus of the present embodiment,the retarding method is adopted. Therefore, a decelerating electricfield has to be induced between the objective lens and sample. A voltagecausing the potential at the control magnetic path member 133 relativeto the potential at the yoke magnetic field member 132 to be negative isapplied to the control magnetic path member 133. The voltage is fed froma control magnetic path power supply 136. A voltage causing a potentialdifference from the potential at the booster magnetic path member 116 tobe negative is applied from a stage power supply 141 to the stage 140.Therefore, the electron beam 110 having passed through the boostermagnetic path member 116 is rapidly decelerated to reach the surface ofthe sample. Since the landing energy of a primary beam is determinedsolely with the potential difference between the electron source 111 andstage 140, if voltages to be applied to the electron source 111 andstage 140 respectively are controlled into predetermined values, thelanding energy can be controlled into a desired value irrespective ofthe voltages to be applied to the booster magnetic path member 116 andaccelerating electrode 131.

For a better understanding, if the relationships among the controlvoltage values for the foregoing components are expressed withequations, the equations are described as follows:

Electron source<sample<control magnetic path member<yoke member whosepotential is approximately equal to 0 V<booster magnetic pathmember  (1)

Electron source<accelerating electrode whose potential is approximatelyequal to 0 V<booster magnetic path member  (2)

Therefore, when the voltages to be applied to the accelerating electrode131 and booster magnetic path member 116 respectively are set to valuesthat are positive relative to the potential at the electron source 111,the electron beam 110 can rapidly pass through the electron opticalsystem 102. The probe diameter of the electron beam 110 on the samplecan be decreased.

However, a decelerating action on the electron beam 110 exerted betweenthe electromagnetic superposition type objective lens 123 and samplehinders a focusing action of the lens. Therefore, the electromagneticsuperposition type objective lens 123 is requested to exert an intensebeam focusing action. By approaching the electromagnetic superpositiontype objective lens 123 to the sample, the electron beam 110 can befocused more thinly. The electromagnetic superposition type objectivelens 123 is therefore requested to exert the intense focusing action ata distance immediately above the sample.

FIG. 2 shows axial magnetic field distributions on an objective lenswith the control magnetic path member and an objective lens without it,and also shows the positional relationship among the magnetic polemembers in the electromagnetic superposition type objective lens in thepresent embodiment. In the left part of FIG. 2, the curvature of each ofcurves, which are drawn with a solid line and a dashed linerespectively, in the direction of the axis of abscissas expresses amagnetic flux density distribution on the axis (nearly aligned with theray axis of a primary electron beam). The axis of ordinates indicatesheights in the objective lens. The curve drawn with the solid line isconcerned with the objective lens with a third magnetic pole, and thecurve drawn with the dashed line is concerned with the objective lenswithout the third magnetic pole. Since the intensity of a lens action isnearly proportional to the degree and sharpness of the magnetic fluxdensity distribution, the lens action of the electromagneticsuperposition type objective lens can be thought to be exerted at aposition associated with the peak of the curve shown in FIG. 2. In theright part of FIG. 2, a solid line depicting an electron beamschematically expresses a section of a primary electron beam thatundergoes the lens action of the objective lens with the third magneticpole, and a dashed line depicting an electron beam schematicallyexpresses a section of a primary electron beam that undergoes the lensaction of the objective lens without the third magnetic pole. In theschematic diagram of the right part of FIG. 2, the booster magnetic pathmember, yoke member, and control magnetic path member are shown as afirst magnetic pole, a second magnetic pole, and a third magnetic polerespectively.

In the arrangement of the magnetic poles in the objective lens shown inthe schematic diagram of the right part of FIG. 2, the third magneticpole can be disposed at a position closer to a sample than a position inthe related art. Therefore, the lens action exerted position of theobjective lens can be more greatly approached to the sample than thatcan in the related art. In the case of a charged particle beam apparatusadopting the retarding method, a negative high voltage is conventionallyapplied to a sample in order to induce a retarding electric field, and avoltage (typically, a ground potential) higher than the voltage appliedto the sample is applied to the second magnetic pole. Therefore, thedistance between the second magnetic pole and sample cannot help beingset to a long distance that does not bring about electrical discharge.Therefore, the conventional second magnetic pole cannot be approached tothe sample as close to the sample as the third magnetic pole in thepresent embodiment is.

In the electromagnetic superposition type objective lens of the presentembodiment, since a voltage nearly identical to a retarding voltage isapplied to the third magnetic pole, the objective lens is devoid of adrawback of electric discharge between a sample and an electrode. Thegap between the third magnetic pole and sample can be narrowed.Therefore, a position at which an intense lens action is exerted can bemore closely approached to the sample than it is conventionally. Since anegative high voltage equivalent to the retarding voltage is applied tothe control magnetic path member 133, the control magnetic path member133 has to have a structure, which can withstand a high voltage, inrelation to the yoke member 132.

The third magnetic pole is functionally equivalent to a separatedmagnetic path on the side of the bottom of the conventional secondmagnetic pole. As mentioned previously, when a magnetic path isseparated, a degree of concentration of a magnetic flux on each of upperand lower magnetic poles rises. An objective lens that exerts an intensefocusing action on the electron beam 110 can be realized. As a result,the electron beam 110 can be focused more thinly. Eventually,high-resolution microscopic observation is enabled.

For the foregoing reason, the electromagnetic superposition typeobjective lens of the present embodiment can balance a short focallength of a lens and a focusing action.

Even in the electromagnetic superposition type objective lens of thepresent embodiment, there is a limitation in decreasing the workingdistance. The limitation is determined with the upper limit of theintensity of a lens action. The intensity of a lens action becomeslarger along with an increase in an amount of current to be fed to thecoil 134. However, since the yoke member 132, control magnetic pathmember 133, and booster magnetic path member 116 are magneticallysaturated, if the amount of exciting current is increased, the peak ofan axial magnetic field becomes obtuse. If the peak disappears, thefocusing action of the electromagnetic superposition type objective lens123 deteriorates. High-resolution microscopic observation is disabled.The shortest distance between the electromagnetic superposition typeobjective lens 123 and sample making it possible to avoid thedeterioration of the focusing action is the lower limit of the workingdistance, and shall be called the shortest focal length in the presentembodiment.

For adjustment of the electron optical system 102, an exciting currentfor the objective lens may have to be adjusted according to variouscontrol parameters for the optical system. For example, when the landingenergy of the electron beam 110 is changed, the magnitude of excitationhas to be adjusted based on a degree of adjustment to which the landingenergy is adjusted. In FIG. 3, the dependency of the shortest focallength on the landing energy of an electron beam is shown by comparingthe objective lens in the present embodiment with the conventionalobjective lens. A solid line indicates the dependency of the shortestfocal length of the objective lens with a third magnetic pole, and adashed line indicates the dependency of the shortest focal length of theobjective lens without the third magnetic pole. Domains on the uppersides of the solid line and dashed line correspond to domains ofin-focus points. As seen from FIG. 3, as long as the landing energyremains unchanged, the shortest focal length of the objective lens ofthe present embodiment including the third magnetic pole can be moregreatly shortened than that of the conventional objective lens withoutthe third magnetic pole. This is because when the focusing action on theelectron beam 110 is intensified by approaching the peak of a sharpaxial magnetic field to a position immediately above a sample, themagnetic saturation of the first magnetic pole can be avoided. Owing tothe constitution of the electromagnetic superposition type objectivelens of the present embodiment, an electron beam whose landing energyranges from 50 eV to 10 keV can be focused by the electromagneticsuperposition type objective lens having the ability to focus a beam.

The secondary particles 115 derived from irradiation of a primary beamhave a negative polarity, and are therefore accelerated due to apotential difference between the sample 114 and booster magnetic pathmember 116. The resultant secondary particles reach the top of theelectromagnetic superposition type objective lens 123. The secondaryparticles 115 having passed through the booster magnetic path member 116to which a high voltage is applied are rapidly decelerated. Thereafter,the secondary particles 115 reach the upper reflective member 118 andcollide with the secondary-particle collision surface 126. This resultsin tertiary particles 147. In a main body of the central detector 122disposed by the side of the upper reflecting member, an attractingelectric field is induced by a central fetching power supply 148. Thereemitted tertiary particles are fetched into the detector with thestrong electric field. Thus, a top-view image can be obtained.

An axial detector (a multi-channel plate, axial scintillator, orsemiconductor detector) may be substituted for the upper reflectingmember 118 and central detector 122.

A primary electron beam focused using the foregoing electromagneticsuperposition type objective lens is swept over a sample. Secondarycharged particles derived from the sweep are detected and imaged by thehost computer 104. Thus, microscopic observation with a higherresolution than the conventional one is enabled.

Embodiment 2

In relation to the present embodiment, an example in which the presentinvention is applied to a review SEM will be described below.

FIG. 4 is an overall constitution diagram of the review SEM of thepresent embodiment. An iterative description of components whoseoperations and capabilities are identical to those of the componentsshown in FIG. 1 will be omitted in order to avoid a complication.

The review SEM shown in FIG. 4 broadly includes: an electron opticalsystem 102 formed in a vacuum housing 101; an electron optical systemcontrol device 103 disposed on the perimeter of the electron opticalsystem; a host computer 104 that controls the control units included inrespective control power supplies and controls the whole of theapparatus on a centralized basis; an operator console 105 connected tothe control device; and display means 106 including a monitor on whichan acquired image is displayed. The electron optical system controldevice 103 includes a power unit that feeds a current or a voltage toeach of the components of the electron optical system 102, and signalcontrol lines over which control signals are transmitted to therespective components.

The components of the electron optical system 102 are nearly identicalto those of the electron optical system described in conjunction withFIG. 1. A difference lies in that the electron optical system 102includes a detecting capability for a shaded image. What is referred toas the shaded image is an image that has shades thereof enhanced andthat is obtained by discriminating or detecting the azimuth angles andelevation angles of secondary electrons and reflected electrons that aregenerated from a sample to be inspected (a sample image having lightsand darks associated with concave and convex parts of the surface of asample). Using the shaded image, a defect can be efficiently detected.The electron optical system 102 of the review SEM of the presentembodiment includes as discriminating means, which discriminates theazimuth angles and elevation angles of secondary particles, tworeflecting members of a lower reflecting member 117 and an upperreflecting member 118, and a left detector 120, a right detector 121,and a central detector 122 that detect collateral (tertiary) particles119 reemitted due to collision of secondary particles with thereflecting members. The lower reflecting member 117 is disposed betweenan electromagnetic superposition type objective lens 123 and a deflector112. The lower reflecting member 117 is formed with a conical metalmember and has a left collision surface 124 and a right collisionsurface 125, with which the secondary particle collide, formed on theflank thereof. The upper reflecting member 118 is formed with adisk-like metal member having a passage opening, through which a primarybeam passes, formed therein. The bottom of the upper reflecting member118 realizes a secondary-particle reflecting surface 126. The disposedpositions of the left detector 120, right detector 121, and centraldetector 122 are not limited to those shown in FIG. 4 but may bealtered. For example, if an axial detector is disposed on thesecondary-particle reflecting surface of the upper reflecting member118, the same capability as the capability of the central detector 122can be realized. If an axial detector is disposed on each of the leftcollision surface 124 and right collision surface, nearly the samecapabilities as those of the left detector 120 and right detector 121can be realized. If an electromagnetic superposition type deflector (E×Bdeflector) is disposed on the ray axis of a primary electron beam, theprimary electron beam 110 is not deflected but tertiary particlesemitted from the secondary-particle reflecting surface can be guided tothe central detector 122.

The secondary particles 115 derived from irradiation of a primary beamhave a negative polarity and are therefore accelerated due to apotential difference between the sample 114 and booster magnetic pathmember 116. The secondary particles then reach the top of theelectromagnetic superposition type objective lens 123. The secondaryparticles 115 having passed through the booster magnetic path member 116to which a high voltage is applied are rapidly decelerated.High-velocity components (reflected electrons) contained in thesecondary particles have the trajectory thereof separated from thetrajectory of low-velocity components, and collide with the leftcollision surface 124 and right collision surface 125 of the lowerreflecting member 117. Using the electromagnetic superposition typeobjective lens of the present embodiment, the trajectory separation canbe realized and both a contrast and a resolution of a shaped image canbe improved. A voltage for electric-field formation to be used to guidethe tertiary particles 119, which are derived from collision of thehigh-velocity components of the secondary particles 115, into the leftdetector 120 and right detector 121 is fed from a left power supply 142or right power supply 143 to the left collision surface 124 or rightcollision surface 125. At this time, the number of reflected electronsto be fetched into each of the left detector 120 and right detector 121can be controlled. The left power supply 142 and right power supply 143may be integrated into one unit in order to bring the left collisionsurface 124 and right collision surface 125 to the same potential.However, this makes it impossible to control the number of reflectedelectrons. Further, a voltage for electric-field formation to be used tofetch the guided reflected electrons into the detector is fed from aleft fetching power supply 144 or a right fetching power supply 145 tothe left detector 120 or right detector 121.

Reflected electrons advance from the sample 114 toward the lowerreflecting member 117 while being rotated by a magnetic field induced bythe electromagnetic superposition type objective lens 123. Inconsideration of the rotation caused by the magnetic field, coordinatesrepresenting each of positions on the lower reflecting member 117 withwhich the reflected electrons collide are associated with azimuth anglesat which the respective reflected electrons are emitted from the sample.Therefore, when the left collision surface 124 and right collisionsurface 125 are disposed in consideration of a magnitude of rotationcaused by the magnetic field, the coordinates may be associated witheach of concave and convex parts of the surface of the sample.

The secondary particles 146 having the reflected electrons (strictlyspeaking, the high-velocity components of secondary particles) separatedtherefrom reach the upper reflecting member 118 located on the side ofthe electron source 111 at a shorter distance than the distance in whichit is located away from the lower reflecting member 117. The secondaryparticles collide with the secondary-particle collision surface 126,whereby tertiary particles 147 are generated. In the main body of thecentral detector 122 disposed by the side of the upper reflectingmember, an attracting electric field is induced by the central fetchingpower supply 148. The reemitted tertiary particles are fetched into thedetector with the strong electric field. Thus, a top-view image can beacquired concurrently with an irregularities image of the surface of asample.

The electron optical system of the review SEM of the present embodimentincludes an assistant electrode for secondary-electron focusing on theside of the electron source 111 away from the electromagneticsuperposition type objective lens 123. The assistant electrode is formedwith a conductor plate having an opening through which the electron beam110 passes. The magnitudes of a retarding voltage and an acceleratingvoltage are controlled so that a majority of secondary electrons emittedfrom a sample will pass through the opening. Since diffusion of thesecondary electrons is suppressed by the assistant electrode, ahigh-contrast sample image having different lights and darks associatedwith the concave and convex parts of the surface of the sample can beacquired.

However, when a resist film or an insulating film is inspected in theprocess of forming an LSI, electrification or damage occurs due toirradiation of a charged particle beam for image formation. Due to theelectrification, the trajectory of secondary electrons may change andluminous flecks (shading) may appear in an observation image. In theconstitution of the apparatus of the present embodiment, asecondary-particle detector is located at a position, at which thedetector is axially symmetrical to the ray axis of a primary electronbeam, in order to discriminate azimuth angles of secondary particles. Ifa sample is electrified, the ray axis of the trajectory of the secondaryparticles is shifted relatively from the center axis of the detector.Shading occurs on such an occasion. If a shaded image is enhanced inorder to improve the sensitivity in detecting a defect, an adverseeffect of the shift of the trajectory of secondary electrons on theobservation image is intensified. The shading is likely to occurreadily. At this time, when only higher-velocity components areseparated from the secondary particles through focusing control by theassistant electrode so that the higher-velocity components will collidewith the left collision surface 124 and right collision surface 125, theshading can be suppressed. In other words, when high-resolution andhigh-contrast SEM observation is implemented in a state devoid of theshading and damage, an inspection method that is superior in detectionsensitivity and a detection speed can be provided. In addition to beamlanding, an amount of beam current carried by the primary electron beamhas to be appropriately determined in line with an object ofobservation.

The scanning electron microscope of the present embodiment can implementautomatic control in two operating modes, that is, an operating mode(review mode) in which a defect image is rapidly acquired and anoperating mode (length measurement mode) in which the length of afabricated pattern is measured or the fabricated pattern is inspected.

Two selection buttons Review Mode and Length Measurement Mode and abutton Electrification Cancel are always displayed on the display screenof the display means 106. A user of the apparatus can select any of thebuttons using the operator console 105. Further, an image processingunit is incorporated in the host computer 104. If a surfacepotentiometer is included, a degree-of-electrification distribution on awafer can be measured and a degree-of-electrification distributionfunction can be stored in the host computer 104. If a Z sensor isincluded, the distance between the sample 114 such as the wafer and theelectromagnetic superposition type objective lens 123 can be measuredall the time. Pieces of information on parameters that should bespecified in the electron optical system control device, a stage controldevice, and the image processing unit in association with the operatingmodes are stored in the host computer 104. If necessary, the informationis transmitted to the electron optical system control device 103.

When shading occurs, if the operation of the apparatus is switched tothe electrification cancel mode, the shading can be removed. When theuser of the apparatus depresses the Electrification Cancel button,voltages to be applied to the assistant electrode interposed between theyoke member 132 and lower reflecting member 117 and to the lowerreflecting member 117 are changed. Thus, the conditions forsecondary-particle detection dependent on the electrified state of asample are satisfied. Eventually, an image having shading removedtherefrom can be produced.

The foregoing constitution is the minimum constitution of the review SEMfor implementing the present embodiment. For example, a condenser lensthat helps focus an electron beam or a Faraday cup that measures a beamcurrent may be included in order to accomplish the capabilities of thepresent embodiment. For example, when the condenser lens is interposedbetween the accelerating electrode 131 and upper reflecting member 118,the condenser lens can help focus the electron beam. Further, when acurrent limiting diaphragm is interposed between two stages of condenserlenses, the beam current and the spread of a beam in the objective lenscan be mutually independently controlled. Thus, the condenser lenses canhelp focus the electron beam. The deflector 112 generally falls into anelectrostatic type and an electromagnetic type.

In the review mode, a defect image is acquired according to a proceduredescribed below.

(1) A desired wafer is loaded into the apparatus.

(2) The wafer is aligned.

(3) The electron optical system is moved to a defective pointrepresented by coordinates and an in-focus point is located.

(4) A defect observation image is acquired.

For acquiring the defect observation images of multiple points on thewafer, the steps (3) and (4) are repeated. The procedure is effectivemeans for collecting a large number of defect observation imagesquickly.

If the precision in coordinates representing a defective point is foundto be insufficient at the step (3), the apparatus executes the flow fromstep (5) to step (8) described below so as to detect accuratecoordinates representing a defective point. Eventually, a defect imageis acquired.

(5) The optical magnification of the electron optical system is madelower that that in the state established at the step (3).

(6) An in-focus point is located at the same position. If necessary, anelectron-beam irradiation area is finely adjusted by adjusting theposition of the stage or shifting an image.

(7) A low-magnification observation image is acquired, and is subjectedto image processing in order to identify the defective point.

(8) The optical magnification of the electron optical system is madehigher than that designated at the step (5).

(9) A defect observation image is acquired.

For acquiring defect observation images of multiple points on the wafer,the steps (3) to (9) are repeated.

If a defective point cannot be identified merely by performing imageprocessing at the step (7), a defect observation image is acquiredaccording to a procedure described below.

(10) The electron optical system is moved to the position of a dieadjoining a defective point which is represented by coordinates, and anin-focus point is located.

(11) A low-magnification observation image is acquired.

(12) The electron optical system is moved to the defective pointrepresented by coordinates, and an in-focus point is located.

(13) A low-magnification observation image is acquired, and comparedwith the observation image acquired at the step (11) in order toidentify the defective point.

(14) The optical magnification of the electron optical system is raisedin order to acquire an image of the identified defective point.

For acquiring defect observation images of multiple points on the wafer,the steps (10) to (14) are repeated. When the apparatus executes thesteps (10) to (14), the apparatus can collect defect observation imageswhile flexibly coping with the precision in coordinates representing adefective point or the size of the defect.

In the length measurement mode, an observation image of a fabricatedpattern is acquired according to a procedure described below.

(1) A desired wafer is loaded in the apparatus.

(2) The wafer is aligned.

(3) The electron optical system is moved to an observation pointrepresented by coordinates, and an in-focus point is located.

(4) An observation image of a fabricated pattern is acquired.

For acquiring observation images of fabricated patterns at multiplepoints on the wafer, the steps (3) and (4) are repeated. The procedureis effective means for quickly collecting a large number of observationimages of fabricated patterns.

If the precision in coordinates representing an observation point isfound to be insufficient at the step (3), an observation image isacquired according to a procedure described below.

(5) The wafer is aligned again.

(6) The electron optical system is moved to the alignment pointrepresented by coordinates, and an in-focus point is located.

(7) An alignment observation image is acquired, and an observation pointrepresented by coordinates is aligned through image processing.

(8) The electron optical system is moved to the observation pointrepresented by coordinates, and an in-focus point is located.

(9) An observation image of a fabricated pattern is acquired.

For acquiring observation images of multiple points on the wafer, thesteps (6) to (9) are repeated.

For assessing the shape of a fabricated pattern, an observation image ofthe fabricated pattern is acquired according to a procedure describedbelow.

(10) The electron optical system is moved to an observation point, whichis represented by coordinates, in a die adjoining a position at which animage is acquired at the step (9), and an in-focus point is located.

(11) A reference observation image is acquired.

(12) The electron optical system is moved to an observation pointrepresented by coordinates, and an in-focus point is located.

(13) An observation image is acquired and compared with the referenceobservation image acquired at the step (11).

If the precision in coordinates representing an observation point isfound to be insufficient at the step (10) or (12), an observation imageis acquired according to a procedure described below.

(14) The wafer is aligned again.

(15) The electron optical system is moved to an alignment point on theadjoining die which is represented by coordinates, and an in-focus pointis located.

(16) An alignment observation image is acquired, and an observationpoint represented by coordinates is aligned through image processing.

(17) The electron optical system is moved to a reference observationpoint, which is represented by coordinates, in the adjoining die, and anin-focus point is located.

(18) A reference observation image of a fabricated pattern is acquired.

(19) The electron optical system is moved to an alignment point which isrepresented by coordinates, and an in-focus point is located.

(20) An alignment observation image is acquired, and an observationpoint represented by coordinates is aligned through image processing.

(21) The electron optical system is moved to the observation pointrepresented by coordinates, and an in-focus point is found.

(22) An observation image of a fabricated pattern is acquired andcompared with the reference observation image acquired at the step (18).

For acquiring observation images of fabricated patterns at multiplepoints on the wafer, the steps (15) to (22) are repeated. The procedureis means capable of collecting observation images while flexibly copingwith the precision in coordinates representing an observation point orthe fabricated pattern.

Next, a control method for the electromagnetic superposition typeobjective lens included in the review SEM of the present embodiment willbe described below. In either the review mode or length measurementmode, the focal point of an electron beam has to be controlled using theelectromagnetic superposition type objective lens in order to locate anin-focus point. However, the scanning electron microscope of the presentembodiment cannot largely change the focal position due to suchrestrictions as limitations in the focal length of the electromagneticsuperposition type objective lens or limitations imposed on a detectoraccording to a change in a position on a reflecting member with whichsecondary particles collide.

The factors causing the focal position to largely change are two ofelectrification of a sample and the height of the sample. When thesample electrification causes the large change in the focal position, ifa retarding voltage is finely adjusted, an in-focus point can bedetected without the restrictions of the limitations in the focalposition of the electromagnetic superposition type objective lens andthe limitation imposed on a detector. When the sample height causes thelarge change in the focal position, an in-focus position can be detectedaccording to, for example, a technique described below.

(1) An electrostatic chuck is used to reduce a warp in the surface of awafer at the time of immobilizing the wafer on the stage.

(2) The height of the stage is controlled in line with the thickness ofthe sample.

(3) An exciting current for the coil included in the electromagneticsuperposition type objective lens is changed.

(4) A voltage to be applied to the booster magnetic path member ischanged.

Owing to the foregoing constitution, reflected electrons can bediscriminated and detected, and an image having a shade contrast thereofenhanced can be acquired. Eventually, a microscopic foreign matterhaving shallow irregularities can be highly sensitively detected.

Embodiment 3

In relation to the present embodiment, an example of a constitution of areview SEM including an electrostatic adsorption device will bedescribed below.

FIG. 5 is an overall constitution diagram of the review SEM of thepresent embodiment. As for the components other than an electrostaticchuck, since the operations and capabilities thereof are identical tothose of the components shown in FIG. 4, an iterative description of thecomponents other than the electrostatic chuck will be omitted.

The review SEM of the present embodiment has a sample stage thereofprovided with an electrostatic chuck mechanism. In addition to signalcontrol lines and a power unit for the electron optical system 102, astage control device is incorporated in the electron optical systemcontrol device 103. The stage control device includes a power unit thatfeeds a current or a voltage to the components of the electrostaticchuck, and signal control lines over which control signals aretransmitted to the respective components.

The electrostatic chuck mechanism includes a dielectric layer 200 and aninternal electrode 201, which are incorporated in the stage 140, and aninternal electrode power supply 203 that applies a voltage across theinternal electrode 201 and wafer 114. Along with application of avoltage, electrostatic adsorption force is generated between theinternal electrode 201 and wafer 114, and the wafer 114 is adsorbed bythe generated force. Depending on an adsorption method, theelectrostatic chuck generally falls into a Coulomb force type and aJohnson-Rabeck force type. The Coulomb force type can reduce a currentflowing across the internal electrode 201 and wafer, and theJohnson-Rabeck force type can reduce a potential difference between theinternal electrode 201 and wafer. In general, the electrostatic chuckfalls into a mono-polar method and a bipolar method according to theinternal electrode 201 located below the dielectric layer 200. Thebipolar method can keep charges, which are accumulated on the dielectriclayer 200 and wafer 114, neutral.

The stage 140 is provided with a contact electrode 202 to be used tobring the stage into contact with a wafer. A potential causing apotential difference from the potential at the booster magnetic path tobe negative is developed at the contact electrode 202. When thepotential difference between the control magnetic path member 133 andcontact electrode 202 falls within ±100 V, the potential differencebetween the wafer and control magnetic path can be controlled. Owing tothe control of the potential difference, the efficiency in focusing aprimary beam or collecting and discriminating secondary particles can becontrolled. Eventually, a high-resolution top-view image and ahigh-resolution shaded image can be obtained.

When an object of observation is a large flat-plate sample such as awafer, if the electrostatic chuck is adopted as the sample stage, a warpof the sample is suppressed, and an observation area including anelectron-beam irradiation area is flattened. Since a variance in the gapbetween the wafer and control magnetic path is suppressed, the magneticpoles in the objective lens can be approached to the sample accordingly.The electromagnetic superposition type objective lens of the presentinvention capable of balancing a short focal length of a lens and afocusing action thereof is highly compatible with the electrostaticchuck. When the electromagnetic superposition type objective lens andelectrostatic chuck are used in combination, an irradiation opticalsystem whose working distance is shorter than that of the chargedparticle optical system described in relation to the embodiments 1 and 2can be realized. Thus, a primary beam can be more thinly focused, thebeam diameter can be reduced, and the efficiency in collecting anddiscriminating secondary particles can be improved. Eventually, ahigh-resolution top-view image and a high-resolution shaded image can beobtained.

FIG. 6A and FIG. 6B show a variant of the review SEM including theelectrostatic adsorption device. FIG. 6A is an overall constitutiondiagram of the review SEM, and FIG. 6B is an illustrative diagramshowing the structure of an electromagnetic superposition type objectivelens including a temperature control mechanism for a control magneticpath member. The electrostatic chuck dissipates heat when adsorbing thewafer 114. In particular, the Johnson-Rabeck force type electrostaticchuck dissipates much heat. Therefore, after the wafer is adsorbed bythe electrostatic chuck, the wafer 114 is thermally expanded until thetemperature is stabilized. When the wafer is thermally expanded, thedrift of a beam landing position occurs, and a blur appears in anobservation image. In addition, the alignment of the wafer is broken.The electron optical system cannot be moved to a desired point on thewafer represented by coordinates, and automatic control in the reviewmode or length measurement mode cannot be implemented. In order tosuppress the drift, it is necessary to manage the temperature of thewafer.

In general, the electrostatic chuck mechanism includes a temperaturecontrol mechanism. The temperature of the stage 140 can be controlled bypouring an air or liquid into a pipe 300 in the electrostatic chuck.However, measurement of the temperatures of the wafer 114 andelectrostatic chuck has revealed that a temperature difference isobserved between the wafer and electrostatic chuck. This is attributableto the inflow of radiant heat into the wafer. The electromagneticsuperposition type objective lens 123 acts as a heating source becausethe electromagnetic superposition type objective lens causes a largecurrent to flow into the coil 134 due to the necessity of exciting astrong magnetic field. In particular, since the control magnetic path inthe electromagnetic superposition type objective lens is opposed to thewafer with a narrow gap between them, the control magnetic path islargely involved with the inflow of radiant heat to the wafer.Therefore, a mechanism for controlling the temperature of the controlmagnetic path member is included in the control magnetic path member.

A cooling pipe 301 through which a coolant flows is embedded in thecontrol magnetic path member 133. In the present embodiment, water isadopted as the coolant. When the control magnetic path member is cooled,the control magnetic path member has the capability to shield theradiation of heat dissipated from the electromagnetic superposition typeobjective lens to the wafer. Thus, the temperature difference betweenthe wafer and electrostatic chuck can be suppressed. As a result, thedrift of a beam landing position and misalignment of the wafer can besuppressed.

In the review SEM of the present embodiment, the control magnetic pathmember 133 and stage 104 are provided with thermometers 302 and 303respectively. Temperature information measured by the thermometer 302 istransmitted to the host computer 104 over a signal transmission linethat is not shown. A coolant feeding pipe 304 and a pump 306 serving ascoolant circulation means are connected to the cooling pipe 300 for theelectrostatic chuck. A mass-flow controller 305 is disposed as flow rateadjustment means on the path of the coolant feeding pipe 304. Whenreceiving the temperature information measured by the thermometer 302 or303, the host computer 104 controls the mass-flow controller 305 so asto appropriately control the flow rate of the coolant flowing throughthe cooling pipes 300 and 301. Thus, the temperatures of the controlmagnetic path member 133 and stage 104 are controlled. By including theabove mechanism, the temperatures of the control magnetic member 133 andstage 104 can be highly precisely controlled, and the thermal expansionof the wafer can be managed. The precision in alignment of the wafer isupgraded to 500 nm or less. The throughput of automatic control in thereview mode or length measurement mode is markedly improved.Incidentally, as the coolant, aside from a liquid such as water, an airwhose heat capacity is large, such as, helium (He) may be adopted.Nevertheless, the same advantage as the advantage of water can beprovided. However, the liquid is preferred because of the high coolingeffect.

Owing to the review SEM of the present embodiment, the gap between thecontrol magnetic path member and the booster magnetic path or wafer canbe set to a value smaller than the conventionally adopted value.Further, the performance of the electromagnetic superposition typeobjective lens is improved. Eventually, a higher-resolution top-viewimage and a higher-resolution shaded image can be acquired.

Embodiment 4

In relation to the present embodiment, an example in which the presentinvention is applied to a scanning electron microscope including a stagetilting mechanism will be described below. FIG. 7A is an overallconstitution diagram of the scanning electron microscope, and FIG. 7B isan enlarged view of an electromagnetic superposition type objective lenscapable of coping with stage tilting.

The scanning electron microscope of the present embodiment includes anelectron optical system 102 formed in a vacuum housing 101, an electronoptical system control device 103 disposed on the perimeter of theelectron optical system, a host computer 104 that controls control unitsincluded in respective control power supplies and controls the whole ofthe apparatus on a centralized basis, an operator console 105 connectedto the control device, and display means 106 including a monitor onwhich an acquired image is displayed. The electron optical systemcontrol device 103 includes a power supply unit that feeds a current ora voltage to each of the components of the electron optical system 102,and signal control lines over which control signals are transmitted tothe respective components.

The capabilities and operations of a primary electron beam irradiationsystem and a secondary-particle detection system are nearly identical tothe capabilities and operations described in conjunction with FIG. 1A.An iterative description will be omitted.

The scanning electron microscope of the present embodiment has a stagetilting capability. The stage 104 includes a stage tilting mechanism anda motor that drives the tilting mechanism. A tilt angle of the stage iscontrolled by the host computer 104 via the electron optical systemcontrol device 103. Since the scanning electron microscope has the stagetilting capability, the objective lens has a shape like the one shown inFIG. 7B. The electromagnetic superposition type objective lens shown inFIG. 7B includes, similarly to the objective lens shown in FIG. 1B, ayoke member 132, a booster magnetic path member 116, a control magneticpath member 133, and a coil 134. However, the bottom of the yoke member132 is different from that of the yoke member shown in FIG. 1B, and isconical. This is intended to prevent the bottom of the objective lensfrom colliding with the sample placement surface of the stage or asample during stage tilting. The control magnetic path member 133 isdisposed along the conical surface of the bottom of the yoke member 132.The control magnetic path member 133 is supported by an insulatingsupporting member so that the distance between the bottom of the yokemember 132 and the control magnetic path member 133 will remainconstant, though the supporting member is not shown. The slope of theconical surface of the bottom of the yoke member 132 (apex angle) isdesigned in line with the maximum tilt angle of the stage.

Since the electromagnetic superposition type objective lens of thepresent embodiment applies a voltage, which is nearly equal to thepotential at a sample, to the control magnetic path member 133, thepotential difference between the stage 140 and control magnetic pathmember 133 is smaller than the conventional one. Therefore, even whenthe distance from a wafer to the bottom of the objective lens variesdepending on a position on the wafer, a potential distribution betweenthe wafer and the bottom of the objective lens will not take on anabnormal shape (will not be asymmetric). Further, since the potentialdifference is smaller than the conventional one, electric dischargebetween the sample 114 and control magnetic path member 133 can besuppressed. Therefore, oblique observation of a sample with a higherresolution than a conventional one can be realized. When the boostermagnetic path member 116 is shielded with the control magnetic pathmember 133, an electric field that efficiently attracts secondaryparticles can be induced in a detector disposed in a sample chamber bythe side of the electron optical system 102. Eventually, a high-contrastobservation image can be acquired.

In the electromagnetic superposition type objective lens of the presentembodiment, the booster magnetic path member 116 has a conical shapehaving the sample surface side thereof sharpened. When theelectromagnetic superposition type objective lens is approached to thesurface of a sample with the distal part thereof thinned, a magnitude ofthe action of a tilted electric field in the sample chamber, which isderived from tilting of the stage, on an electron beam can be reduced,and the tendency of the spot of the probe-like electron beam toward anon-point shape can be suppressed. Further, even when the stage istilted, the booster magnetic path member 116 sucks secondary particlesso that the secondary particles will collide with the left collisionsurface and right collision surface of the lower reflecting member andthe upper reflecting member. As a result, a high-contrast top-view imageand a high-contrast shaded image can be acquired. Since the shortestdistance between the stage and booster magnetic path member 116 isshortened due to tilting of the stage, a voltage to be applied to thebooster magnetic path member 116 has to be approached to the potentialat the control magnetic path member along with an increase in the tiltangle.

Using the scanning electron microscope of the present embodiment, ahigh-performance scanning electron microscope capable of balancinghigh-resolution and high-contrast observation performance and a stagetilting capability can be realized.

The present invention can be applied to an electron microscope or ionmicroscope application apparatus requested to permit high-resolution andhigh-contrast observation.

What is claimed is:
 1. A charged particle beam apparatus, comprising: astage for placing a sample thereon; a detector detecting secondarycharged particles generated due to irradiate a primary charged articlebeam to the sample; an objective lens that focuses the primary chargedparticle beam on the sample and having an opening through which theprimary charged particle beam passes; and a power supply unit applying anegative voltage to the sample, wherein the objective lens includes: afirst magnetic pole member that is disposed around the opening and has aterminal portion at a sample side thereof that functions as an uppermagnetic pole member of the objective lens; a second magnetic polemember that supplies a magnetic flux to the first magnetic pole memberand is formed with a hollow interior; a coil that is disposed within thesecond magnetic pole member and supplies a magnetic flux to the secondmagnetic pole member; and a third magnetic pole member that is disposedbetween the stage and the second magnetic pole member, has the openingand functions as lower magnetic pole member of the objective lens, andwherein a potential lower than that of the second magnetic pole memberis supplied to the third magnetic pole member.
 2. The charged particlebeam apparatus according to claim 1, further comprising: means forsupplying a retarding potential to the sample, wherein a potentialhigher than the retarding potential is supplied to the third magneticpole member.
 3. The charged particle beam apparatus according to claim2, wherein a potential difference between a potential at the sample anda potential at the third magnetic pole member is within 100V.
 4. Thecharged particle beam apparatus according to claim 3, wherein thepotential at the third magnetic pole member is equal to the potential atthe sample.
 5. The charged particle beam apparatus according to claim 2,wherein an accelerating potential for accelerating the primary chargedparticle beam is applied to the first magnetic pole member.
 6. Thecharged particle beam apparatus according to claim 1, furthercomprising: means for electrically isolating the second magnetic polemember and the third magnetic pole member from oath other.
 7. Thecharged particle beam apparatus according to claim 1, wherein the secondmagnetic pole member is brought to a ground potential.
 8. The chargedparticle beam apparatus according to claim 1, wherein a bottom of thesecond magnetic pole member has a conical shape with the opening, andwherein the third magnetic pole member is realized with a magnetic platedisposed in parallel with a conical surface of the conically-shapedbottom with a predetermined gap left from the conical surface.
 9. Thecharged particle beam apparatus according to claim 1, furthercomprising: an electrostatic adsorption device that holds the sample.10. The charged particle beam apparatus according to claim 9, whereinthe electrostatic adsorption device includes: an internal electrode thatis opposed to the sample with a dielectric between them; a contactelectrode that applied a retarding voltage to the sample; and means forretaining a potential difference between a potential at the contactelectrode and a potential at the third magnetic pole member at a valuefalling within-±100V.
 11. The charged particle beam apparatus accordingto claim 1, further comprising: a cooling member for the third magneticpole member.
 12. The charged particle beam apparatus according to claim1, further comprising: means for acquiring a shaded image of a portionof irradiation of the primary charged particle beam.
 13. The chargedparticle beam apparatus according to claim 1, wherein the third magneticpole member has two magnetic plates of an upper magnetic plate and alower magnetic plate; and wherein the lower magnetic plate is brought toa same potential as a potential at the sample.